This application claims priority of Korea patent Application No. 2000-87014, filed on Dec. 30, 2000.
(a) Field of the Invention
The present invention relates to a manual valve used in a hydraulic pressure control system for an automatic transmission.
(b) Description of the Related Art
Generally, a conventional automatic transmission for a vehicle includes a multi-stage gear shift mechanism connected to a torque converter, and a plurality of friction elements actuated by hydraulic pressure under control of a hydraulic pressure control system for selecting a gear stage of the gear shift mechanism.
In such automatic transmissions, the hydraulic pressure control system includes a pressure regulating means for controlling a level of hydraulic pressure generated by a hydraulic pump, manual/automatic shift control means for performing shift operation, hydraulic pressure control means for adjusting responsiveness and shift quality by smoothing shift operation, hydraulic pressure distributing means for distributing the pressure from the hydraulic pressure control means to appropriate friction elements, and damper clutch control means for controlling operation of a damper clutch of a torque converter.
The gear shift control is achieved by the friction elements being selectively and differently applied by hydraulic pressure from the distribution means and cooperation of on/off and duty control solenoid valves, such that a constitution and control method of a hydraulic control system depends on particular power trains adapted by car makers and how the power trains are controlled.
FIG. 1 shows a conventional hydraulic control system for an automatic transmission.
When a torque converter 2 is driven, a hydraulic pump 4 generates hydraulic pressure required for controlling the torque converter 2 and shift control and for lubrication. The hydraulic pressure generated by the hydraulic pump 4 is supplied to pressure regulating means, damper clutch control means, and reducing means, and to pressure control means via manual/automatic shift control means to be modulated to a shift control pressure. The shift control pressure controlled by the pressure control means is supplied to the friction elements as operating pressure via switching means and fail-safe means. The hydraulic pressure is directly supplied from the manual/automatic control means to N-R control means, and then to the friction elements.
Describing more in detail, the pressure regulating and damper clutch control means includes a regulator valve 6 for uniformly regulating hydraulic pressure generated by the hydraulic pump 4, a torque converter control valve 8 for supplying the regulated hydraulic pressure to the torque converter 2 and for adjusting the regulated hydraulic pressure to be suitable for lubrication, a damper clutch control valve 10 for controlling a damper clutch to improve a power transmission efficiency of the torque converter 2.
The reducing means comprises a reducing valve 12 for reducing hydraulic pressure to be lower than the line pressure. Part of the hydraulic pressure reduced by the reducing valve 12 is directed to the damper clutch control valve 10 and the regulator valve 6 as control pressure, and the rest is supplied to first, second and third pressure control valves 14, 16 and 18 that are controlled by first, second and third solenoid valves S1, S2 and S3, respectively.
The manual/automatic shift control means includes a manual valve 20 cooperating with a shift selector lever (not shown). The hydraulic pressure fed to the manual valve 20 is, in accordance with the operation of the shift selector lever, directed to the first, second and third pressure control valves 14, 16, 18 as control pressure, or directly to first and second switch valves 22 and 24, the first and second fail-safe valves 26 and 28, and the N-R control valve 30 as control pressure and operating pressure to be fed to the fiction elements.
In the above described hydraulic control system, when an engine is operating, line pressure of a certain degree is required for supplying fluid as lubricant to rotating elements regardless of the range that the manual valve 20 is in.
Furthermore, when the manual valve is displaced in a parking range P or a neutral range N, line pressure identical to or lower than that required for forward ranges D, 3, 2 and L is required to prepare for the shift operation into forward and reverse ranges. Line pressure required for the reverse range R is generally higher than that for the forward ranges.
However, since the shift range of the manual valve 20 is arranged in the order of P, R, N, D, 3, 2, and L, that is, since the reverse range R is arranged between the parking and neutral ranges P and N, it is practically difficult to satisfy the above requirements.
Accordingly, some hydraulic control systems have been designed such that no line pressure is formed in the parking range P. However, in these cases, when the engine is operated for a long time in the parking range P, rotating elements suffer a lack of lubrication since there is no line pressure.
Therefore, it has become a trend that line pressure is basically formed in the parking and neutral ranges P and N so as to supply lubricant to the rotating elements.
FIGS. 14a and 14b shows a conventional manual valve which is designed to form line pressure in the parking and neutral ranges P and N.
A valve body of a manual valve is provided with a first port 200 for receiving hydraulic pressure from a regulator valve, a second port 202 for supplying the hydraulic pressure fed through the first port 200 to parking and neutral range pressure lines, a third port 204 for supplying the hydraulic pressure fed through the first port 200 to drive, second, and low range pressure lines, fourth and fifth ports 206 and 208 for supplying hydraulic pressure fed through the first port 200 to a reverse range pressure line, and an exhaust port EX for exhausting the hydraulic pressure fed to the fourth and fifth ports 206 and 208.
A valve spool 210, being movably disposed in the valve body in accordance with the manipulation of the shift selector lever, includes a first land 214 formed proximate to a connector 212, positioned between the second and third ports 202 and 204 in the parking range P, and positioned on one side of the third port 204 in other ranges R, N, D, 2 and L; a second land 216 for communicating the second or third port 202 or 204 with the first port 200 in all ranges except for the parking and reverse ranges P and R; and a third land 218 for communicating the first port 200 with the fourth and fifth ports 206 and 208 in the reverse range R.
Also, the valve spool 210 is further provided with an exhaust hole 220 formed from the connector 212 to the second land 216, a first release opening 222 formed between the first and the second lands 214 and 216 in a vertical direction with respect to an axis of the valve spool 210, and a second release opening 224 formed proximal to the connector 212 between the first land 214 and the connector 212.
In the parking range P, the hydraulic pressure supplied to the manual valve through the first port 200 is directed to the second port 202 and the exhaust hole 220 through the first release opening 222. In the reverse range R, the first port 200 communicates with the fourth and fifth ports 206 and 208, and in the neutral range N, the first port 200 communicates with the second port 202. In the forward ranges D, 2 and L, the first port 200 communicates with the second and third ports 202 and 204.
In this conventional manual valve, since the hydraulic pressure fed from the hydraulic pump 4 is used for lubrication and hydraulic pressure for a parking and neutral range, there is no problem in lubricating the rotating members in the parking and neutral ranges P and N. However, since the hydraulic pressure is fed through the second release opening 224, the eccentric force is applied to the valve spool 210. Therefore, when the system is used for a long time, the valve spool 210 may be worn in one side. This results in leakage of fluid and thereby a lowering of the line pressure.
Furthermore, when the eccentric force is continuously applied to the valve spool 210, a land thereof may be caught on an end of a port, thereby disturbing the movement of the valve spool 210.
Accordingly, a very strict quality control is required to provide enough structural strength of a manual valve.
Furthermore, the valve spool is made through a complicated process. For example, holes 220 and 224 must be formed by drilling, a cap for obstructing the exhaust hole 220 is required and then the connector must be connected. This causes the manufacturing costs to be increased and the productivity to be deteriorated.
Therefore, the present invention has been made in an effort to solve the above problems.
It is an objective of the present invention to provide a manual valve of a hydraulic pressure control system capable of forming line pressure at parking and neutral ranges P and N to improve lubrication, and to reduce the manufacturing costs by simplifying the manufacturing process.
To achieve the above objective this invention provides a manual valve of a hydraulic pressure control system for an automatic transmission of a vehicle, comprising:
a valve body provided with a line pressure receiving port, a P/N range port for supplying hydraulic pressure in more than one of parking range P and neutral range N, a plurality of hydraulic pressure supplying ports and a plurality of exhaust ports; and
a valve spool slidably inserted into the valve body and having a plurality of valve lands, a first valve land of said plurality of valve lands having an exhaust groove depressed toward a neighboring land; wherein:
each width of the line pressure receiving port and the P/N range port is smaller than each diameter of said plurality of valve lands, whereby a tight seal is maintained when each of the line pressure receiving port and the P/N range port is blocked by said plurality of valve lands; and
each width of the plurality of hydraulic pressure supplying ports is greater than each diameter of said plurality of valve lands, whereby hydraulic pressure reserved in each of said plurality of hydraulic pressure supplying ports is exhausted through the exhaust groove when blocked by the first land.